Polyploidy, a significant catalyst for speciation and evolutionary processes in both plant and animal kingdoms, has been recognized for a long time. However, the exact molecular mechanism that leads to polyploid formation, especially in vertebrates, is not fully understood. Our study aimed to elucidate this phenomenon using the zebrafish model. We successfully achieved an effective knockout of the cyclin N-terminal domain containing 1 (cntd1) using CRISPR/Cas9 technology. This resulted in impaired formation of meiotic crossovers, leading to cell-cycle arrest during meiotic metaphase and triggering apoptosis of spermatocytes in the testes. Despite these defects, the mutant (cntd1−/−) males were still able to produce a limited amount of sperm with normal ploidy and function. Interestingly, in the mutant females, it was the ploidy, not the capacity of egg production that was altered. This resulted in the production of haploid, aneuploid, and unreduced gametes. This alteration enabled us to successfully obtain triploid and tetraploid zebrafish from cntd1−/− and cntd1−/−/− females, respectively. Furthermore, the tetraploid-heterozygous zebrafish produced reduced-diploid gametes and yielded all-triploid or all-tetraploid offspring when crossed with wild-type (WT) or tetraploid zebrafish, respectively. Collectively, our findings provide direct evidence supporting the crucial role of meiotic crossover defects in the process of polyploidization. This is particularly evident in the generation of unreduced eggs in fish and, potentially, other vertebrate species.

中文翻译：

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基于斑马鱼cntd1敲除，通过破坏减数分裂交叉频率形成不同的多倍体

多倍体是植物和动物界物种形成和进化过程的重要催化剂，长期以来一直受到人们的认可。然而，导致多倍体形成的确切分子机制，特别是在脊椎动物中，尚不完全清楚。我们的研究旨在使用斑马鱼模型来阐明这一现象。我们利用CRISPR/Cas9技术成功实现了细胞周期蛋白N端结构域1（cntd1）的有效敲除。这导致减数分裂交叉的形成受损，导致减数分裂中期细胞周期停滞并引发睾丸精母细胞凋亡。尽管存在这些缺陷，突变体（cntd1−/−）雄性仍然能够产生有限数量的具有正常倍性和功能的精子。有趣的是，在突变的雌性中，改变的是倍性，而不是产卵能力。这导致产生单倍体、非整倍体和未减少的配子。这种改变使我们能够分别从 cntd1−/− 和 cntd1−/−/− 雌性中成功获得三倍体和四倍体斑马鱼。此外，当与野生型（WT）或四倍体斑马鱼杂交时，四倍体杂合斑马鱼分别产生减少的二倍体配子并产生全三倍体或全四倍体后代。总的来说，我们的研究结果提供了直接证据，支持减数分裂交叉缺陷在多倍化过程中的关键作用。这在鱼类和其他脊椎动物中未减少的卵的产生中尤其明显。